Magnetic deflecting system for braun tubes



E. RUSKA MAGNETIC DEFLECTING SYSTEM FOR BRAUN TUBES July 23, 1940.

2 Sheets-Sheet 1 Filed July l, 1936 ,LWE

July 23, 1940.

E. VRUSKA 2,20,,939

MAGNETIC DEFLECTING SYSTEM FOR BRAUN TUBES Filed July 1, 193s 2 Sheets-Sheet 2 Patented July 23, 194s 2,208,939

UNITED STATES PATENT OFFICE MAGNETIC DEFLECTING SYSTEM FOR BRAUN TUBES Ernst Ruska, Berlin-Zehlendcri', Germany, as-

signor to the firm Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application July 1, 1936, Serial No. 88,487 In Germany July 16, 1935 2- Claims. (Cl. 25il--157) The invention relates to magnetic deflecting the customary constructions the end conductors coils intended for cross-controlling the ray in of both half coils together form a more or less Braun tubes especially for image scanning and closed circuit. If this circuit is completely traimage producing purposes. versed by current flowing in the same direction,

5: Deflecting coils for Braun tubes, insofar as the resulting field would act upon the ray like they are not wound on ferromagnetic cores, are one collector coil. Since, however, the two halves either formed as flat, round coils or as rectanguof the circuit are traversed by current in oppolar coils, the end conductors of which, lying in site directions, the field component parallel to the a plane perpendicular to the ray, are under certube axis disappears in the entire plane passing l0 tain conditions bent around the neck of the tube. through the tube axis and separating the two In the case of rays of large diameter and when coil halves from each other. On the other hand, greater deflecting angles are involved in the magthe field in the vicinity of each individual end nectic cross control system, such great enlargeconductor retains the nature of a collector field ments and distortions of the focal spot occur especially in the center of its arc.

i=5 when such coils are used that the television im- The controlled ray as it issues from the coil ages received for example become very unsharp approaches very close to the end conductors. at the outer borders. The end conductors exert their greatest deflection The object of the invention is to improve the at that instant and also carry the heaviest curdeflecting coils so as to be able to deflect thicker rent so that the field of the end conductors also bundles of rays to greater angular amounts and becomes particularly effective. This field exerts 20 thus to obtain appreciably clearer pictures while a supplementary ray-collecting action which at the same time shortening the tubes. manifests itself in an undesirable enlargement of The cathode ray during the deflecting procedthe spot (over-focussing of the bundle of rays) ure is acted upon not only by the deflecting fields in the border portions of the image field although per se which are produced by the principal sides the spot may be correctly and sharply focussed 25 of the coils extending parallel along the axis in the center of the image. This phenomenon of the t b b also by the fi P du ed y becomes all the more evident when two pairs of the end conductors. Spot enlargements and disperpendicularly placed deflecting coils are used, tortions thereof occur primarily when the deince then the deflection effected by one pair of fle fi in the plane pfi p 0 the coils directs the ray towards the center of the axis of the ray is not homogeneous. In order to end c nd t r of th other pair of coils, p d om e us a fie d a possible, the In order to obviate these influences it is proangular cross section thereof, in accordance with d, in accordance with the present invention, the invention, s ve th S pe a lotlgitlldito dispose the end conductors at a greater dis- 5 nally extended, e. a. small, rectangle, an the tance from the tube than corresponds to the sepadjacent side conductors of two half coils are aration of the effective end conductor. The sep- SO p With their Small Sides facing each aration of the side conductors, in order to achieve other that they fo a Compact longitudinally as great sensitivity as possible, must be made as extended current conduct ay Sihce, small as is permitted by the deflection desired. an ever, the lines of fOTCeT even in 13011 Systems Of This limit is governed, in the case of deflectional compact longitudinally extended cross section, do systems dispgsed i Vague, b t contacting of not join c mpl ly Within the two oppositely the ray with the end conductors at the issue side cated coil cross sections, dispersion, according to of the second pair of half coils and, in the case the invention, is additionally effectively prevented of deflectional systems disposed exteriorly of a by not making the current layer of the coil sides um, by the wiping of the ray on the Wall constant but p a y by s ng the same symof the tube. In both cases, in accordance with metrically outwardly from the value obtaining in the inv ntion, the end conductors are 1 d off the center of each coil side, and making said rise outwardly to a greater extent than this limit. taper in a particularly rapid manner at the outer- In that case the ray, even in its outermost de- .70 most ends. Improvement is effected even if the flected position, is still within the domain of the current is kept constant over the length of the strength of a small longitudinal magnetic field winding cross section and if supplementary windsince its smallest distance from an end conductor ings are applied only to both ends of the windings. never decreases to an extent compared with the A further distortion of the field is caused by difference of the distances from both conductors. the end conductors of the deflecting coils. In The inductivity of the system is not increased 55 to a harmful extent by increasing the loop of the end conductors since the magnetic flux embraced thereby is equal to zero owing to the direction of current flow in the two half coils.

Embodiments of the invention are shown in the drawings, wherein:

Fig. 1 is a diagrammatic representation of the customary shape of coil.

Figs. 2, 3, 4 and 10 each show cross sections through the deflecting coils perpendicular to the axis of the tube.

Fig. 5 is a diagrammatic view of two deflecting coils of the invention.

Figs. 6, 6a, '7, 7a, and 8, 8a show the coils during the process of their formation.

Fig. 9 shows a further embodiment, viewed in the direction of the axis.

Fig. 1 shows two coil halves with side conductors l and end conductors 2. The field produced -by the side conductors is not homogeneous in the deflecting space since the lines of force do not run parallel but are curved at the outer portions of the field. This fault also occurs partially when the cross section of the two side conductors is, in accordance with the invention, so formed that a rectangle is produced with the large side of the rectangle extending in the direction of the axis of the coil.

In accordance with the invention, as shown in Fig. 2, the winding is so arranged that the current layer in the side conductors l is made to increase outwardly. The desired distribution of the current layer while keeping the winding cross section constant is achieved by interposing insulating strips of suitable thickness. In order to render the field uniform, a uniformly wound coil, may also be used as shown in Fig. 3, with the side conductors l disposed somewhat obliquely to each other whereby the field in the deflecting cross section 3 is rendered homogeneous. A further embodiment, shown in Fig. 4, consists in so providing a supplementary winding 5 that it strengthens the field on the outer side of the side conductor.

' In order to reduce the influence of the end conductors, as shown in Fig. 5 they are given such a shape that they are removed as far as possible from the deflecting field. The coils which have a rectangular cross section are made as thin as the heating of the coil or the exigencies of the winding processpermit, making allowance for subsequent bending. The coil after being wound on a mandrel in flat (plane) shape as shown in Fig. 6 is either impregnated and wrapped, or merely wrapped and bent in the manner shown in Figs. 7 and 8. The end conductors 2 of both half coils may be elliptical or rectangular. Likewise the longitudinal sides I of the coil may be bent ofi in such a manner over against the end conductors that end conductors of bent fiatedged type are produced.

If two crossed pairs of coils of this type are to be used for the same height of ray, then the axial expansion of one pair of coils must be made smaller, by an amount equal to double the height of the windings of the end conductors than those of the other pair, in order that the coil sides may interengage with each other. In order that the two pairs of coils do not difier too much with respect to their length (unequal ampere turns) the height of the end conductors should be as small as possible. Nevertheless the height of the side conductors may be artificially increased by inserting strips, e. g. of insulating material, be- 5 tween the layers at definite distances. The longer pair of deflecting coils which embraces the other pair of coils is preferably used for line deflecting purposes in order to secure approximately the same ampere turn values for both coils notwithstanding the presence of unequal deflecting angles.

The influence of the end conductors may be completely obviated while at the same time avoiding loss of sensitivity in the coil system if, in accordance with Fig. 9, coils are used in which the electrical axis does not cut the axis of the tube at right angles but merely by-passes at right angles to the tube axis at a given distance therefrom. In that case the longitudinal sides pertaining otherwise to two half coils are united into one coil 6, whereas the other likewise adjacent longitudinal sides of both half coils constitute the second coil 1. Such coils may be wound on a rectangular mandrel 8 in a simple manner. The mandrels 8 may remain in the coils and may be united into a framework of finished form by means of screws or pins and adapted to surround the neck 9 of the tube.

A further possibility of obviating the harmful 30 influences due to the end conductors resides in applying an equalizing winding 4 (Fig. 10) adjacent to the end conductors 2 but traversed in opposite direction by the current. By suitably connecting the principal and equalizing coils in series, the deflecting current may be used direct in the principal coil. The coil, compared with the principal coil, should be made so broad that its magnetic flux only slightly decreases the deflecting field of the principal coil.

The compensation of the end conductor ampere turns need not amount to 100% since even a partial equalization is of advantage.

Removal of the disturbing field produced by the end conductors may be effected in accordance with the invention even without efiecting a separate homogenization of the field of the side conductors.

I claim:

1. In combination with a cathode ray tube, opposed defiecting coils having end windings and flat side windings parallel to the axis of said tube, so arranged that adjacent flat sides of said opposed coils are coplanar, and having end windings arranged with greater separation from said tube than said side windings, said flat side windings having an increasing current layer away from the axis of said tube.

2. In combination with a cathode ray tube having deflecting coils including end and side conductors, said side conductors being normal to the deflecting field, means for minimizing the field about the end conductors only of said coils comprising compensating windings on the same side of said tube and disposed closely adjacent, and adapted to neutralize the field due to, the end conductors only, said deflecting coils and compensating windings being connected in series.

ERNST RUSKA. 

